Shock mitigating spring and detent pedestal

ABSTRACT

A personnel protecting pedestal has two telescoping elements biased apart by a coil spring and held together by a limit stop. A detent prevents telescoping of the elements toward each other until a predetermined shock loading is reached. The force needed to compress the spring is less than the force needed to release the detent, so that upon occurrence of a shock wave, the spring distributes the velocity associated with the shock wave over a period of time longer than the duration of the shock wave, thus reducing the velocity and, therefore, the overall acceleration on the load to be protected.

United States Patent Inventors Frank I. Whitten Bethesda; Charles E.Strother, Rockville; Joseph Gosswein, Bethesda, Md.

Appl. No. 763,145

Filed Sept. 27, 1968 Patented Mar. 30, 1971 Assignee The United Statesof America as represented by the Secretary of the Navy SHOCK MITIGATINGSPRING AND DETENT PEDESTAL 3 Claims, 9 Drawing Figs.

US. Cl. 248/20, 248/358, 267/178 Int. Cl. F16f 15/00 Field ofSearch267/(178), 1; 248/20, 21, 401, 24, 402, 358, 350, 403; 188/102 PrimaryExaminerEdward C. Allen Assistant Examiner-J. Franklin Foss Attorneys-L.A. Miller, 0. E. Hodges and A. Sopp ABSTRACT: A personnel protectingpedestal has two telescoping elements biased apart by a coil spring andheld together by a limit stop. A detent prevents telescoping of theelements toward each other until a predetermined shock loading isreached. The force needed to compress the spring is less than the forceneeded to release the detent, so that upon occurrence of a shock wave,the spring distributes the velocity associated with the shock wave overa period of time longer than the duration of the shock wave, thusreducing the velocity and, therefore, the overall acceleration on theload to be protected.

Patented March 30, 1971 3,572,621

2 Sheets-Sheet 1 3 LOAD 'l' INVENTORS 1 FRANK I. WHITTEN F 6 2 CHA RLESE. STROTHER JOSEPH assswzuv AT'TOR N E YS Patented March 30,19113,572,621

2 Sheets-Sheet 2 lg AT REST SHOCK /a 3A. FIG. 35. FIG. 30.

' STATIONARY 1 FREE FALL /LOAD\ /LoAo\ COMPRESS EXPAND 39 STOP II IIENGAGES I II T 19 AT REST FIG. 30. FIG. 35. a. 3E

VELOCITY, FREE FALL INVENTORS G- F'RANK I. WHITTEN CHARLES E. STROTHERJOSEPH GES'SWEIN BY ATTORNEYS SHOCK MITIGATING SPRING AND DETENTPEDESTAL The invention described herein may be manufactured and used byor for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

BACKGROUND AND SUMMARY device constructed according to the principles ofthe present invention employsonly two telescoping elements, a coil.spring, a stop and a simple detent,to provide effective shockmitigation of a load such as personnel and equipment. The device of thepresent inventionis intended primarily for personnel protection onboatsor land vehicles susceptible to shocks from beneath caused by explosionsor slamming of the vehicle.

The device of the invention provides shock mitigation by enablingrelative movement between thetelescoping elements at a much loweracceleration, lower velocity and longer time than the movement of theshock displaced deck or vehicle floor. The distance of travel of thetelescopingelements and the force of the spring are chosen so that theshock-caused deck motion is nearly spent as the spring approaches fullcompression. Therefore, the protected load continues moving under theforce of the spring and the load inertia until the spring expands to thelimit stop. The load may then free-fall to its initial resting place.

It is, therefore, among the objects of the invention to provide: Simpleand inexpensive shock protection apparatus; effective shock mitigationwithout use of fluid damping; shock mitigation devices of easilyrepairable nature for protection of personnel and equipment on air, landand sea vehicles susceptible to shock by explosion or slamming; alightweight shock absorbing device easily deployable on craft singly orin groups for load protection.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects, as well as featuresand advantages of the present invention, will be better understood byreferring to th accompanying drawings in which:

FIG. I is a view in longitudinal cross section of a shock mitigatorconstructed in accordance with the principles of the invention, in theform of a seat and pedestal;

FIG. 2 is a view in modified transverse cross section of a landing orriverine craft employing shock mitigators according to the invention ina group;

FIGS. 3a-f are explanatory diagrams of 'the shock mitigator of theinvention in various positions in a'shock absorbing cycle; and i FIG. 4is a graph of velocity vs. time for explaining the relation between deckmotion and motion ofa load protected by the device of the invention asthe result of-shock acting onthe deck from below. 1

DETAILED DESCRIPTION Referring to FIG. 1, a shock mitigation deviceconstructed in accordance with a preferred embodiment of the inventioncomprises a lower telescoping element 11 for mounting on a base or deck,and an upper telescoping element 13 movable within element 11. Bothelements 11 and 13 may be tubular or A cagelike in construction and, asshown, may be-hollow cylinders each having a plurality of perforations15 in their respective walls for free and unrestricted passage of airfrom within and without.

Atop the upper element 13 is a seat 17 or other load support. The lowerend of the element 13 terminates, in at least one portion thereof, in alongitudinal slot 19, having at its upper end a chamfered surface 20.Another portion of the upper element 13 has a longitudinal groove 21which does not extend to the termination of the element 13, but ends atan upward facing internal shoulder 23.

At the upper end of the lower telescoping element 11 is a transverseaperture 25 for receiving therethrough a detent 27. The inner end of thedetent engages the chamfered portion 20 of theslot 19. The detent 27 isbiased by a spring 29 adjustable by screw 31 to appropriate bias. Thescrew, detent and spring are housed in a fitting 33 welded or fastenedto the wall of ele ment 1 l in any suitable manner.

'Also located at-the upper end of the element 11 is another aperture 35for receiving a bolt 37 which acts as a limit stop for the inner element13 by virtue of engagement with sufficiently hard to at least supportthe load under lg.

In FIG. 2 shock mitigation devices of the invention are shown mounted ona watercraft 41. Thesidewalls of the craft may be provided with fittings43 for supporting shock mitigation 45 of essentially the same design, asthat shown in FIG. I. The mitigators 45 are secured to fittings43 attheir base. A hole is drilled through the base and fitting to enablepassage of a rod or cable therethrough, the cable being attached at itsupper end to the element 13 and at its lower end, to a loadsupportingbench 49.

Comparing FIGS. 1 and 2, and as is explained herein, the operation ofthe shock mitigating devices is the same although in FIG. 2 the loaddepends from each of the devices. Of course, the FIG. 2 arrangement maybe expanded upon in that as many shock mitigating devices may beemployed as desired for load protection.

In assembling the device according to the invention, the detent pressureand spring characteristics are chosen so that in relation to theexpected velocity/time displacement of the vehicle or watercraft due toshock, the detent releases at a higher acceleration than theacceleration that the spring induces on the load. For example, where l00to 200 g. shocks are expected, and the load is a 200 lb. man, the detentmay be adjusted to releaseat about 5 or 6 g., and the spring induce anacceleration of about 3 g. on the load. The travel between telescopingelements should be such that the spring will not fully compress untilthe velocity of the pedestal is approximately the same in absolute valueas that of the vehicle being displaced.

OPERATION Referring to FIGS. 3a-e and 4, the operation of the deviceaccording to the invention, FIGS. 1 and 2, will be explained in relationto its location on a watercraft as affected by an underwater explosion.In FIG. 3a, the device is at rest under force of gravity, 1 g., thedetent is adjusted to release at, say 5 g., the spring when extendedexerts 3 g. against the load and the maximumforce of the spring when atabout full compression is 6 g.

Occurrence of an explosion beneath the watercraft, FIG. 3b, displacesthe craft and entire device (with its load) in unison for a very smallfraction of a second, the detent 2S releasing at 5 g. Thus the forceimparted to the load (e.g. a person in chair 17)' does not exceed 5 g.even though the force on the deck of the craft may be I00, 200 g., etc.

Afier detent release, the deck moves relative to the load as opposed bythe soft, 3 g. spring (FlG. 3c). The travel distance of telescopingelements 11, 13 is sufficient to prevent bottoming of the spring 39prematurely. When the spring bottoms (reaching maximum compression),FIG. 3d, the load is essentially stationary or moving at a tolerable lowvelocity and the maximum velocity of the craft deck has already beenpassed.

As shown in FIG. 4 in which the deck and load" curves of velocity vs.time are so legended, the bottoming of the spring 39 is indicated asoccurring at 6 g. After bottoming, the velocity of the deck furtherdecreases while the load, FIG. 3e, is moved under the approximate 3 g.to 6 g. force of the expanding spring. It is recalled that the spring issufiiciently strong to more than support the load. Therefore, thevelocity of the load-increases slowly under the expansion of the softspring at about a 3 g. to 6 g. rate for a considerable time after thedeck motion becomes negligible, as indicated in FIG. 4.

Eventually the spring fully expands, FIG. 3f, at which point the stop 37engages shoulder 23 bring the motion of the telescoping elements 11, 13to a halt. The load, if not attached to upper telescoping element 13, isshown in FIG. 3f as continuing its motion in free flight after theelements l1, l3 stop moving. If the load represents a person sitting onelement 13, the person free falls at 1 g. until returning to contactwith the element. Consequently, the load does not undergo greater thanabout 6 g. of slow acceleration and g. impact at any time during shockdisplacement of the watercraft.

It is to be understood that the invention is not limited to the exactdetails of construction shown and described for obvious modificationswill occur to persons skilled in the art.

We claim:

1. Apparatus for mitigating by a free-fall isolation principle theeffect of shock on a load carried by a platform which is displacedessentially upward by shock comprising:

essentially upstanding upper and lower telescoping elements, the lowerelement being attached to the platform, and the upper element carryingin an unattached manner the load to be protected;

each of said telescoping elements comprises a tubular body containing aplurality of venting means through which air may freely pass;

spring means positioned internally of both said telescoping elements forbiasing said elements apart;

spring means located in relation to said elements for biasing saidelements apart;

the force exerted by said spring means when extended being sufficient tosupport the load;

at least one detent means releasable at a predetermined forcesustainable by the load for holding said elements in an extendedposition exclusive of the spring means, in said predetermined forcebeing greater than the force exerted by the extended spring means on theload;

at least one limit stop means engaging said telescoping elements forlimiting the extent of their movement apart from each other to aposition approximately that of the elements when held by said detentmeans; and

whereby upon occurrence of the shock the elements converge after releaseof the detent means under the load inertia against the resistance of thespring means to a converged position and then diverge under spring forceto the extended position at which the detent means reengages and thelimit stop halts the motion of the elements while the load continues tomove in a free-fall manner, the velocity/time ratio of the load therebybeing substantially less than that of the platform.

2. Apparatus according to claim 1 wherein said detent means comprises:

an elongated recess located axially of the upper element and having adownward facing chamfer at the upper end of the recess;

a detent element for engaging the chamfer;

a spring for biasing the detent against the chamfer;

means for ad'ustingothe bias of the spring; and

means attac ed said lower telescoping element for mounting said detent,spring and said means for adjusting.

3. Apparatus according to claim 2 wherein said limit stop meanscomprises:

an axial groove in said upper telescoping element and terminating at itslower end in a shoulder; and

means attached to the lower telescoping element for extending into thegroove and for engaging said shoulder.

1. Apparatus for mitigating by a free-fall isolation principle theeffect of shock on a load carried by a platform which is displacedessentially upward by shock comprising: essentially upstanding upper andlower telescoping elements, the lower element being attached to theplatform, and the upper element carrying in an unattached manner theload to be protected; each of said telescoping elements comprises atubular body containing a plurality of venting means through which airmay freely pass; spring means positioned internally of both saidtelescoping elements for biasing said elements apart; spring meanslocated in relation to said elements for biasing said elements apart;the force exerted by said spring means when extended being sufficient tosupport the load; at least one detent means releasable at apredetermined force sustainable by the load for holding said elements inan extended position exclusive of the spring means, in saidpredetermined force being greater than the force exerted by the extendedspring means on the load; at least one limit stop means engaging saidtelescoping elements for limiting the extent of their movement apartfrom each other to a position approximately that of the elements whenheld by said detent means; and whereby upon occurrence of the shock theelements converge after release of the detent means under the loadinertia against the resistance of the spring means to a convergedposition and then diverge under spring force to the extended position atwhich the detent means reengages and the limit stop halts the motion ofthe elements while the load continues to move in a free-fall manner, thevelocity/time ratio of the load thereby being substantially less thanthat of the platform.
 2. Apparatus according to claim 1 wherein saiddetent means comprises: an elongated recess located axially of the upperelement and having a downward facing chamfer at the upper end of therecess; a detent element for engaging the chamfer; a spring for biasingthe detent against the chamfer; means for adjusting the bias of thespring; and means attached to said lower telescoping element formounting said detent, spring and said means for adjusting.
 3. Apparatusaccording to claim 2 wherein said limit stop means comprises: an axialgroove in said upper telescoping element and terminating at its lowerend in a shoulder; and means attached to the lower telescoping elementfor extending into the groove and for engaging said shoulder.